1. Field of the Invention
This invention relates to an image display device having substrates opposed to each other and a plurality of electron sources arranged on the inner surface of one of the substrates.
2. Description of the Related Art
In recent years, there have been demands for image display devices for high-grade broadcasting or high-resolution versions therefor, which require stricter screen display performance. To meet these demands, the screen surface must be flattened and enhanced in resolution. At the same time, the devices must be lightened in weight and thinned.
Flat image display devices, such as a field emission display (hereinafter referred to as FED), are promising as image display devices that fulfill the above requirements. The FED has a first substrate and a second substrate that are opposed to each other with a given gap between them. These substrates have their respective peripheral edge portions joined together directly or by a sidewall in the form of a rectangular frame, thereby constituting a vacuum envelope. Phosphor layers are formed on the inner surface of the first substrate. A plurality of electron emitting elements for use as electron sources that excite the phosphor layers to luminescence are provided on the inner surface of the second substrate.
A plurality of spacers for use as support members are arranged between the first and second substrates in order to support the atmospheric load that acts on these substrates. In displaying an image on this FED, an anode voltage is applied to the phosphor layers, and electron beams emitted from the electron emitting elements are accelerated and run against the phosphor layers by the anode voltage. Thereupon, the phosphors glow and display the image.
According to the FED of this type, the size of each electron emitting element is on the micrometer order, and the distance between the first substrate and the second substrate can be set on the millimeter order. Thus, this image display device, compared with a cathode ray tube (CRT) that is used as a display of an existing TV or computer, can achieve higher resolution, lighter weight, and reduced thickness.
In order to obtain practical display characteristics, in the image display device of the type described above, the anode voltage should preferably be set to several kilovolts or more with use of phosphors that are similar to those of a conventional cathode ray tube. In view of the resolution and the properties and manufacturability of the support members, however, the gap between the first and second substrates cannot be made very wide and must be set to 1 to 2 mm or thereabouts. When electrons that have high acceleration voltage run against the phosphor surface, moreover, secondary electrons and reflected electrons are generated on the phosphor surface.
If the space between the first substrate and the second substrate is narrow, the secondary electrons and the reflected electrons that are generated on the phosphor surface run against the spacers between the substrates, so that the spacers are charged with electricity. With the acceleration voltage of the FED, the spacers are charged positively, in general. In this case, the electron beams emitted from the electron emitting elements are attracted to the spacers and deflected from their original paths. In consequence, the electron beams are mislanded on the phosphor layers, so that the color purity of the displayed image lowers inevitably.